Electrical circuits



March 1951 v. c. WESTCOTT 2,544,407

ELECTRICAL CIRCUITS Filed May 2, 1946 /NVENTO/? VERNON C wesrcorT Patented Mar. 6, 1951 ELECTRICAL cmoorrs I Vernon C. Westcott, Lincoln, Mass., assignor to Raytheon Manufacturing Company, Newton, Mass'., a corporation of Delaware Application May 2,1946, Serial No. 666,588

This invention relates to electrical circuits, and more particularly to an oscillator.

An object of this invention is to devise an oscillator having a very wide range of oscillation frequencies.

Another object is to devise an oscillating circuit which is capable of producing waves having various wave forms.

A further object is to devise an oscillator which can be used to emphasize selected harmonics of a certain frequency. I I

The foregoing and other objects of the invention will be best understood from the following description of an exemplification thereof, reference being had to the accompanying drawing,

wherein: 1

Fig.1 is a diagrammatic representation of on means for carrying out the invention; and

Fig. 2 is a diagrammatic representationof another means for carrying. out the invention.

Referring to Fig. 1, an electron discharge tube, for example a tetrode, is shown at I, said tube having an anode 2,-a screen grid 3, a control grid and a cathode which is heated to the temperature of thermionic emission by any suitable heating means (not shown). Screen grid 3 is connected through a resistor 6 to a positive B-supply lead I, and is also connected through a condenser 8 to a. grounded lead 9. Cathode 5 is connected through a self-biasing arrangement, com rising a condenser Ill and a resistor II in parallel, to lead 9. Anode or plate 2 is connected to B-supply lead I through an artificial tapped open coil transmission line I2. Line l2 consists of a series inductance I3 having a movable tap I4 thereon, and is so constructed as to provide distributed shunt capacitance I5 therealong. This line is terminated in its characteristic impedance Z0, whereby reflections of waves traveling along 'said line are prevented. Plate 2 is connected, :through a condenser Hi, to one side of a load I1, the other side of said load being connected to the control grid 4. Leak resistor 2| is connected from 'the grid side of condenser 20 to grounded lead 9.

5? In order for oscillations to be established in a tube circuit, it is essential that there be a phase 7 shift of 360 degrees around the system, from the input to the output and back to the input again,

and it is also essential that the gain around the i system be at least equal to unity. If these two 1 Claim. (01. 250-36) conditions be fulfille'd, the system will oscillate at a frequency for which there is a phase shift of 360 degrees around the system, if the system gain for such a frequency is at least equal to unity. There is ordinarily a phase difference of degrees between grid and plate voltages due to the inherent properties of an electron discharge tube, so that if an additional phase shift of 180 degrees can be imparted to a wave by the external system, the required 360 degree shift will be obtained.

Transmission or delay line I2, due to its inductance and capacitance, will impart a phase shift or phase delay to waves traveling down it. For any fixed position of tap I4, there is a certain frequency forv which the phase delay between plate 2 and tap I4 will be exactly 180 degrees, andthe circuit will oscillate at this certain frequency if the gain around the system is greater than unity. Another way of expressing this is, for any fixed position of tap I4, there is a certain frequency at which the time required for a wave, to travel from the plate 2 to the tap I4 will be exactly equal to one-half cycle of this frequency,- or 180 degrees, and the system will oscillate at this frequency. The frequency of oscillation of the system may be varied by moving tap I4, since for each different position of tap I4 there is a certain different frequency at which the proper phase relations for oscillation occur. Since it is possible to make the transmission line as long as desired, and since it is theoretically possible to bring tap I4 infinitely close to plate 2, a broadband oscillator is provided by this invention. An enormous frequency range, such as, for example, from 30 kilocycles to 20 megacycles, may be obtained with a single oscillator and may be utilized in a load device I! of any desired type.

As will be appreciated by those skilled in the art, the required 180 degree phase delay, for any fixed position of tap I4, exists for a certain fundamental frequency and for all odd harmonics of that fundamental. This affords a means whereby various different wave forms may be obtained, from pure sinusoidal to square waves. The transmission line attenuates the lower frequencies less than the higher frequencies, while the resistance I8 attenuates all frequencies equally. Therefore, by moving tap I9 on potentiometer I8 toward the grounded end thereof, the system gain may be made equal to unity for the fundamental frequency and less than unity for the odd harmonics,

3 gain may be made unity or greater for various odd harmonics, whereby these harmonics will also appear in the oscillator output and a distorted sine wave will be produced. The nearer tap I9 is to the transmission line end of potentiometer l8, the more harmonics will be mixed with the fundamental and the nearer to a square wave the oscillator output will be. Therefore, the wave form of the oscillator output may be varied, for any particular fundamental determined by the position of tap M, by the adjustment of tap 19,

It is to be understood that a real transmission line may be used in place of an artificial transmission line, and that the term transmission line in the claim is meant to include such devices as wave guides, concentric lines, and lecher wire systems. In Fig. 2 is shown an exampleof the latter. In Fig. 2, parts similar to those of Fig. 1 have been given the same reference numerals. A lecher wire system, comprising a pair of wires 22 arranged in the form of a circle, COD-r.

nects anode 2 to B-supply lead I. These two wires are connected together at one end by the characteristic impedance Z of the line, while plate 2 is connected to the opposite end of one wire and lead 1 to the opposite end of the other. A sliding contact 23 is connected to control grid Athrough condenser 20, and engages the wire 22 frequency characteristic, terminated at one end in its characteristic impedance and provided along the length thereof with a first movable tap:

which is connected to plate 2. In Fig. 2, the lecher wires are used to provide the phase delay, and the frequency of oscillation is varied by moving contact 23. In Fig. 2, a potentiometer arrangement similar to that of Fig. 1 may be used in the grid feedback connection. This has not been shown, in order to simplify the drawing.

' If desired, in order to obtain low frequencies of output, the lecher wires may be loaded with a piece of iron near their Z0 end, or the lecher wire system may be combined with a delay line of the type shown in Fig. 1, for example, both of these expedients being useful to obtain greater delay than that possible with a lecher wire system.

the other end of said transmission line being connected between said anode and the positive terminal of said source of voltage; and a potentiometer connected at its ends, respectively, to the negative terminal of said source of voltage and to said first movable tap, and provided along the. length thereof with a second movable tap; said second movable tap being connected to said control electrode.

7 'VERNON C. WESTCOTT.

REFERENCES CITED The following references are of record in the file of this patent: v

UNITED STATES PATENTS Hollingsworth et a1. Dec. 24, 1946' 

